1. Field of the Invention
The invention relates in general to an electric device, and more particularly to an electric device avoiding speaker quality being affected by radio frequency signal.
2. Description of the Related Art
Along with the development in science and technology, various electric devices are directed towards the trend of slimness, lightweight and compactness. As the volume of the electric device is reduced, the elements inside the electric device are more intensive and some elements can even be shared. The electric device 900 of FIG. 1 is exemplified below.
Referring to FIG. 1, a functional block diagram of a conventional electric device is shown. The electric device 900 includes an antenna 910, a first power amplifier 920, a filter 930, a baseband converter 940, an audio chip 950, a second power amplifier 960, a speaker 970 and a battery 980. The first power amplifier 920 is electrically coupled to the antenna 910 and the filter 930. The baseband converter 940 is electrically coupled to filter 930. The second power amplifier 960 is electrically coupled to the audio chip 950 and the speaker 970. Besides, the first power amplifier 920 and the second power amplifier 960 are both electrically coupled to the battery 980.
After the antenna 910 receives a radio frequency (RF) signal, the first power amplifier 920 further amplifies and outputs the RF signal to a filter 930. Then, the filter 930 filters the RF signal enhanced by the first power amplifier 920 and transmits the filtered RF signal to the baseband converter 940 for conversing a baseband of the filtered RF signal.
The second power amplifier 960 receives an audio frequency signal from the audio chip 950, and further amplifies and outputs the audio frequency signal to the speaker 970. To avoid the decay of the RF signal, the first power amplifier 920 of the antenna 910 is normally disposed around the antenna 910. This is because if the first power amplifier 920 is disposed too far away from the antenna 910, the RF signal has to travel through a longer path and is more susceptible to the influence of surrounding signals, making the impedance not uniformed and the RF signal decayed. Likewise, to avoid the decay of the audio frequency signal, the second power amplifier 960 of the speaker 970 is also disposed around the speaker 970. Therefore, the first power amplifier 920 and the second power amplifier 960 are preferably disposed around the battery 980. When the first power amplifier 920 and the second power amplifier 960 receive the voltage provided by the battery 980, a part of the RF signal is fed back to the battery 980.
As the battery 980 also provides a working voltage to the second power amplifier 960, the feedback signal fed back to the battery 980 will be transmitted to the second power amplifier 960 via the battery 980 first and then transmitted to the speaker 970 next. That is, the working voltage provided by the battery 980 contains some noise. Normally, a frequency range of a time slot frame of the feedback signal approximately 217 Hz or a frequency multiplication thereof is audible to human ears. Therefore, the user of the electric device 900 will often hear the audio signal outputted by the speaker 970 carrying a noise similar to a high frequency signal.
Under such circumstances, the requirement of slimness, lightweight and compactness in the design the electric device is met by using two batteries to avoid noise, hence jeopardizing the quality of the audio signal or the economy of the volume of the electric device.